Method and apparatus for electrolyzing water

ABSTRACT

A method and an apparatus for electrolyzing water in which electrolysis of water can be carried out while effectively removing scales such as calcium carbonate and by which the service life of electrode can be extended on the order of several years. Repeated in sequence are a step wherein water is subjected to electrolysis while using an electrolytic cell of the membraneless type and a step wherein feed of water through the cell is stopped and an electric potential of reverse polarity is applied between electrodes while water stays stagnant in the cell whereby precipitate deposited on the electrodes during the electrolyzing step is removed by dissolving into stagnant water. Since application of the reverse potential is effected while water stays stagnant in the cell, the surface of the electrodes is free from the influence of turbulence and there is no risk that a layer of strongly acidic water generated at the surface of the electrodes is washed away by water flow. Accordingly, a layer of acidic water of the maximum strength is generated at the electrode-water interface whereby calcium carbonate precipitated on the electrode surface in the electrolysis step is released.

This application is a 371 of PCT/JP95/01310 filed Jun. 30, 1995.

TECHNICAL FIELD

The present invention relates to a method and an apparatus forelectrolyzing water to electrochemically produce alkaline and/or acidicwater. More specifically, the present invention is concerned with amethod and an apparatus wherein water is subjected to electrolysis whileeffectively removing scales, such as calcium carbonate, deposited onelectrodes and electrolytic cell.

BACKGROUND ART

It is believed that hydroxyl ion (OH⁻) enriched alkaline water, which isoften incorrectly referred-to as "alkaline ion water", is useful inhealth maintenance when served as potable water as well as inaccentuating taste when used in cooking or for the preparation ofbeverages such as tea and coffee. Similarly, hydrogen ion (H⁺) enrichedacidic water is known as being suitable for boiling noodles and washingfaces. More importantly, highly acidic water which is obtained byelectrolysis of tap water containing sodium chloride or an aqueoussolution of sodium chloride and which therefore contains effectivechlorine (hypochlorous acid or chlorine gas) has been noted as having astrong germicidal effect.

To produce alkaline and/or acidic water, an apparatus for electrolyzingwater has been used hitherto which is often incorrectly referred--to inthe art as "ion water generator". This apparatus, designed to subjectwater to electrolysis, includes an electrolytic cell having an anode anda cathode. As a direct electric potential is applied between theelectrodes, the hydroxyl ions OH⁻ being present in water due toelectrolytic dissociation of water molecules will donate electrons tothe anode at the anode-water interface and are thereby oxidized to formoxygen gas which is then removed away from the system. As a result, theH⁺ concentration is enhanced at the anode-water interface so that H⁺enriched acidic water is resulted at the anode-water interface. At thecathode-water interface, on the other hand, H⁺ accepts electron from thecathode and is reduced to hydrogen to form hydrogen gas which issimilarly eliminated from the system. As a result, the OH⁻ concentrationis increased whereby OH⁻ enriched alkaline water is generated at thecathode side. When an aqueous solution of sodium chloride is subjectedto electrolysis, chlorine gas is generated at the anode and is dissolvedinto water to form hypochlorous acid.

To preclude alkaline water and acidic water once generated byelectrolysis from being mixed with each other and to take them outseparately, the conventional electrolytic cells are typically providedwith a water-impermeable but ion-permeable membrane 3 arranged betweenan anode plate 1 and a cathode plate 2 as schematically shown in FIG. 1,the electrolytic chamber being divided by the membrane into a flowpath 4for alkaline water and a flowpath 5 for acidic water. The electrolyticcell of this type will be referred-to hereinafter as the "membrane-type"electrolytic cell.

As the electrolytic cell is operated, precipitation of scale 6 comprisedof calcium carbonate, calcium hydroxide, magnesium hydroxide and thelike takes place in the flowpath for alkaline water. Referring to FIG. 2wherein the apparent solubility of calcium carbonate versus pH is shown,the mechanism of scale precipitation will be described with reference tocalcium hydroxide by way of an example. It will be noted from the graphthat under acid conditions, calcium carbonate is dissolved into water inthe form of calcium ions. However, as the pH exceeds 8, the solubilityis rapidly drops thereby giving rise to precipitation of calciumcarbonate. In the electrolytic cell of the membrane type, the scaletends to precipitate predominantly on the membrane 3 rather than on thecathode 2, as shown in FIG. 1. Probably, this is because the porousnature of the membrane promotes precipitation of scale, in contrast tothe cathode generally having a polished specular surface. Since theprecipitates such as calcium carbonate are electrically insulating, theelectrical resistance across the cell is increased thereby lowering theefficiency of electrolysis of the cell. In addition, formation of scaleincreases the flow resistance across the electrolytic cell. Therefore,unless the scale is removed, the electrolytic cell would becomeinoperative soon after a short period of use.

Accordingly, there has been proposed in the prior art to remove theprecipitates by dissolving them into water as disclosed, for example, inJapanese Patent Kokai Publication 51-77584, Japanese Utility Model KokaiPublication 55-91996, Japanese Utility Model Kokai Publication59-189871, and Japanese Patent Kokai Publication 1-203097. According tothis method, a polarity reversal switch 7 is turned over in such amanner that an electric potential of an polarity opposite to the normaloperating polarity is applied between the electrodes to thereby causethe precipitates to dissolve. This method is known in the art as"reverse electrolysis descaling" or "reverse potential descaling"process. The principle of reverse electrolysis descaling is that, uponapplication of electric potential of the opposite polarity, the flowpathfor the alkaline water is changed into acidic conditions whereby thescale such as calcium carbonate is disintegrated into ions to againdissolve into water as will be understood from FIG. 2.

It is believed that in the method described in JP 51-77584, JP 55-91996,and JP 59-189871, application of the reverse polarity potential fordescaling is carried out while water is fed to flow across theelectrolytic cell. However, since the membrane 3 is more or less spacedfrom the electrodes as will be understood from FIG. 1, the stream ofstrongly acidic water which has been generated along the surface of theelectrode 2 (originally acting as the cathode, but now acting as theanode because the polarity of potential is reversed) will be carriedaway by the flow of water flowing through the flowpath so that stronglyacidic water could not reach the membrane as long as it is present inmoving water. Therefore, with this method, the membrane cannot berendered acidic to a degree strong enough to quickly dissolve the scaledeposited on the membrane.

In the method proposed in JP 1-203097, on the contrary, the reversepolarity potential is applied when feed of water to the electrolyticcell is stopped. Obviously, this is to preclude the user frominadvertently drinking water that would otherwise be issued from theelectrolytic cell during the reverse electrolysis descaling. As in thismethod the application of reverse voltage is carried out while flow ofwater is stopped, the hydrogen ions generated at the surface of theinitial cathode 2 (now anode because the potential is reversed) willpermeate through the membrane 3 and will be diffused toward the oppositeflowpath so that acidic water and alkaline water once generated aremixed with each other and are neutralized. As a result, the membranecannot be rendered strongly acidic. According to the experiment carriedout by the present inventors, the pH of the flowpath 4 for alkalinewater did not become less than 3 when the reversed polarity potentialwas applied while flow of water was stopped so that removal of scale wasnot observed even after about two days of application of the reversedpolarity potential.

In this manner, in the "membrane-type" electrolytic cell, it has beendifficult to electrochemically remove the scale even though theso-called reverse electrolysis descaling is carried out. Accordingly, ithas been usual that the life of the electrolytic cells is only from ahalf to one year unless the cells are periodically disassembled and aresubjected to manual mechanical descaling operations. Furthermore, themembrane is unhygienic since it serves as breeding bed for bacteria.

In order to overcome the foregoing disadvantages of the membrane-typeelectrolytic cell, proposed in Japanese Patent Kokai Publication4-284889 is an electrolytic cell which is free from a membrane. Theelectrolytic cell of this type will be referred-to hereinafter as the"membraneless" type electrolytic cell. In the membraneless-type cell,the electrode plates are spaced from one another with a small gap insuch a manner that a laminar flow is established as water flows betweenthe electrodes. Therefore, alkaline water and acidic water as generatedcan be separated from each other without recourse to a membrane.

As the membraneless-type electrolytic cell is not provided with amembrane which is susceptible to deposition of scale, there is anadvantage that less scale is deposited. The formation of scale takesplace primarily on the cathode plate so that scale is extremely small inamount as compared with the membrane-type electrolytic cell. Moreover,the cell is hygienic because of the absence of a membrane which wouldotherwise breed bacteria.

The "membraneless" electrolytic cell of JP 4-284889 is also designedsuch that the reverse polarity potential is applied to carry out theso-called reverse electrolysis descaling in a manner similar to theconventional membrane-type electrolytic cells. Descaling is performedwhile water flow through the cell is maintained. To this end, a pressureresponsive switch is provided to ensure that a polarity reversal switchis turned over to apply the reverse polarity voltage only when thepresence of water pressure is detected.

In this way, in the membraneless electrolytic cell, also, theapplication of reverse polarity potential is carried out while water isflowing through the cell. Accordingly, the layer of strongly acidicwater (e.g., highly acidic water having pH value of less than 1) whichhas once been generated at the surface of the electrode (i.e., the anodewhen the polarity of the voltage is reversed) will be carried away bythe water flow as soon as it is generated and will be mixed with anddiluted by the layer of weakly acidic water having a greater pH value.Furthermore, in the membraneless electrolytic cell, the laminar flow isnot fully developed at the inlet or upstream region of the flowpathdefined between the electrodes so that this region is subject to theinfluence of turbulence. Accordingly, it is difficult to generatestrongly acidic water along the electrode surface located at the inletregion. For these reasons, the scale cannot be satisfactorily removedunless reverse electrolysis descaling is carried out quite frequently.According to the present inventors' experiment, the deposition of scaleis prevented to a practically satisfactory degree when the reverseelectrolysis descaling by application of reverse polarity potential isrepeated for every 4 minutes of electrolysis.

However, to frequently apply the reverse polarity potential for thepurpose of descaling is undesirable because the service life of theelectrodes is drastically shortened. More specifically, the cathode isgenerally made of platinum coated titanium plate. During the course ofordinary electrolysis, the surface of the platinum coating is covered bya film of platinum oxide formed thereon. The film of platinum oxide isstable as long as a minus voltage is applied to the cathode. However,upon application of a plus voltage to the cathode for the purpose ofreverse electrolysis descaling, platinum oxide is reduced into platinumwhereupon it partly dissolves into water in the form of platinum ions.If chlorine ions are present in water, platinum ions will reacttherewith to form highly soluble platinum chloride which then readilydissolves into water. Therefore, the cathode plate is exhausted anddamaged each time the reverse polarity potential is applied. In the casewhere the cathode is made from titanium plate without platinum coatingor from a metal other than platinum, exhaustion of the cathode resultingfrom the reverse polarity potential application would be moresignificant.

In this manner, to increase the frequency of reverse voltage applicationin order to perfectly remove the scale will result in prematureexhaustion of the electrode plates. If to the contrary the frequency ofreverse voltage application is to be limited, the electrolytic cell willsoon become unusable due to deposition of scale. In any case, accordingto the conventional methods, it was therefore impossible to prolong theoverall service life of the electrolytic cell beyond a period on theorder of years.

An object of the invention is to provide a method and an apparatus forelectrolyzing water which permit use of an electrolytic cell for as along period as several years and which, hence, are capable of extendingthe overall life of the cell.

Another object of the invention is to provide a method and an apparatusfor electrolyzing water wherein water is electrolyzed while the scale iseffectively removed and which are capable of extending the life of theelectrodes.

DISCLOSURE OF THE INVENTION

The method for electrolyzing water according to the invention ischaracterized by repeating the steps of:

subjecting water to electrolysis while using an electrolytic cell of themembraneless type; and,

removing precipitates deposited on the electrodes during theelectrolyzing step by stopping feed of water through the cell and byapplying an electric potential of the opposite polarity between theelectrodes while water in the cell stays stagnant to thereby cause theprecipitates to dissolve into stagnant water.

As in this manner the application of the reverse potential is carriedout while feed of water is stopped so that water in the cell staysstagnant, there is no risk that the surface of the electrodes isaffected by turbulence and that the layer of strongly acidic watergenerated at the electrode surface is washed away by the flow of water.Accordingly, a layer of acidic water having the maximum strength isformed at the electrode-water interface. The layer of strongly acidicwater acts to cause flocculent precipitates such as calcium carbonateand the like, which have precipitated on the electrode surface duringthe preceding electrolyzing sequence, to dissolve along theelectrode-water interface. As a result, the physical and chemicalbondage between the electrode and the precipitates is loosened therebypermitting the precipitates to be released from the electrode. Fordescaling, it will suffice that the reverse potential is applied forabout a second. The flocculent precipitates that have thus been releasedfrom the electrode will be readily washed away when feed of water isrestarted and will be discharged out of the cell.

According to the invention, the frequency of reverse potential descalingmay be minimized since in this way the scale is effectively removed. Itwill suffice that the application of the reverse potential is carriedout once a day. Therefore, according to the invention, the service lifeof the electrodes may be extended up to about 7 years.

In another aspect, this invention provides an apparatus for carrying outthe foregoing water electrolyzing process. The apparatus comprises anelectrolytic cell of the membraneless type, a DC power source, areversal switch for reversing the polarity of potential applied betweenthe electrodes, detection means for detecting feed of water through thecell, and control means, having a timer function, for controlling thereversal switch in response to the detecting means. The control meanscontrols the reversal switch in such a manner that a DC potential of apredetermined polarity is applied between the electrodes while water isfed through the cell and that a DC potential of an opposite polarity isapplied between the electrodes at a predetermined timing when feed ofwater through the cell is stopped. The application of the reversevoltage may be carried out everyday at night.

These features and advantages of the invention as well as other featuresand advantages thereof will become apparent from the followingdescription.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional representation of the conventionalmembrane-type electrolytic cell;

FIG. 2 is a graph showing the apparent solubility of calcium carbonateversus pH;

FIG. 3 is a perspective view showing an example of a water processingunit wherein the water electrolyzer according to the invention isincorporated;

FIG. 4 is an exploded perspective view of the unit shown in FIG. 3;

FIG. 5 is an exploded perspective view of the electrolytic cell shown inFIG. 4;

FIG. 6 is a cross-sectional view taken along the line VI--VI of FIG. 5and showing the electrolytic cell as assembled;

FIG. 7 is a cross-sectional view taken along the line VII--VII of FIG.6, with electrodes and spacers being omitted for simplicity;

FIG. 8 is a cross-sectional view taken along the line VIII--VIII of FIG.6;

FIG. 9 is a cross-sectional view taken along the line IX--IX of FIG. 6;

FIG. 10 is an enlarged view showing a part encircled by the circle A inFIG. 7;

FIG. 11 illustrates an exemplary layout of a control and display panelof the water processing unit; and,

FIG. 12 is a block diagram of the control unit of the water processingunit.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will now be described in more detail withreference to the accompanying drawings showing an embodiment of theinvention. In FIG. 3, there is shown a water electrolyzer embodying theinvention as incorporated in a water purifier for domestic use.

Referring to FIG. 3, the water purifier or water processing unit 10 isdesigned for use as it is placed, for example, on a kitchen counter 14equipped with a sink 12. In the illustrated layout, the sink is providedwith a mixing valve 16 of the single-lever type to which hot water froma boiler (not shown) is supplied via a hot water piping 16A and tapwater is applied through a water piping 16B connected to the publicwater line (not shown). Spout 18 of the mixing valve 16 is provided witha faucet adapter 20 wherein a flow control valve mechanism is arranged,the adapter 20 being connected to the processing unit 10 through a tapwater supply hose 22 and a processed water delivery hose 24.

Upon rotating a handle 26 of the adapter 20 into a predetermined angularposition, tap water from the mixing valve 16 will be forwarded throughthe supply hose 22 to the processing unit 10 and water after treatmentwill be returned via the delivery hose 24 to the adapter 20 for deliverythrough an outlet 28. Upon turning the handle 26 into another position,non processed water or a mixture thereof with hot water coming from themixing valve 16 will be directly delivered from the outlet 28 of theadapter 20 upon bypassing the processing unit 10. Connected further tothe processing unit 10 is a drain hose 30 which is adapted to dischargewaste water occurred in the processing unit 10 to the sink 12.

Referring to FIG. 4, the water processing unit 10 is designed andconstructed such that any particulate matters, such as ferrous rust andmicroorganisms, which are born in tap water are first removed byfiltration, that any harmful or undesirable substances such as residualchlorine, trihalomethanes and smelly substances which are dissolved intap water are then removed under the adsorption action of activatedcarbon, and that the thus purified water is further subjected toelectrolysis to produce acidic and/or alkaline water at the user'sdiscretion. To this end, the water processing unit 10 is comprised of afiltration stage 32 wherein a filter (not shown) such as hollow-fibermembrane filter is received, an adsorption stage including an activatedcarbon cartridge 34 wherein fibrous or granular activated carbon isreceived, and an electrolytic cell 36 for generating acidic or alkalinewater. These components parts of the water processing unit are supportedby a base 40 having a bottom plate 38 and are enclosed by an outercasing 42.

Tap water from the mixing valve 16 is forwarded via the supply hose 22to the filtration stage 32, with filtered water being delivered througha hose 44 to the activated carbon cartridge 34. The activated carboncartridge 34 is made of metal such as stainless steel and is provided atits bottom with an electric heater 46. Periodically or in response tothe user operating a switch, the heater 46 is operated to heat theactivated carbon cartridge 34. Upon heating, the activated carbon in thecartridge 34 will be boiled and sterilized and, at the same time,chlorine and trihalomethanes having been adsorbed by the activatedcarbon will be desorbed whereby the activated carbon is regenerated. Atemperature-sensitive three-way valve 50 is disposed at the outlet 48 ofthe cartridge 34 so as to direct hot water and steam generated duringregeneration of activated carbon toward an outlet 52 as well as todirect purified water toward another outlet 54 when the cartridge is notheated. The outlet 52 is connected to the drain hose 30 through hose andjoint (not shown) so as to discharge hot water and steam toward the sink12. The outlet 54 is connected to an inlet of the electrolytic cell 36via a hose, not shown.

Referring to FIGS. 5-10, an embodiment of the electrolytic cell 36 willbe described by way of an example. The electrolytic cell 36 is of themembraneless type and includes an elongated pressure-resistive casing 56made of rigid plastics. As best shown in FIG. 5, the cell 36 isassembled by placing, in sequence, three planar electrodes (i.e., afirst lateral electrode 58, a central electrode 60 and a second lateralelectrode 62) in a recess of the casing 56 with a plurality of plasticspacers 64 sandwiched therebetween, followed by fluid tightly fasteninga cover 66 by screws to the casing 56. Because a pair of lateralelectrodes are arranged on both side of the central electrode 60, thecell 36 of this embodiment advantageously has a parallel twin structure.Each of the electrodes 58, 60 and 62 may be made of titanium platecoated with platinum and may have a size of about 5×13 cm. Preferably,the spacers 64 has a thickness of about 0.5 mm to ensure that theelectrode spacing is equal to about 0.5 mm.

A terminal 68 is fixed to each of the electrodes for electricalconnection to a DC power source via an electric cord. In a mode whereinalkaline water is to be produced, an electric potential of about 8V isapplied in such a polarity that the lateral electrodes 58 and 62 serveas the anode and the central electrode 60 acts as the cathode. Inanother mode wherein acidic water is to be obtained, the electricpotential is applied in a reversed polarity.

As shown in FIG. 6, the casing 56 has an inlet 70 for purified water, afirst outlet 72 for electrolyzed water, and a second outlet 74 forelectrolyzed water, the first outlet operating as the outlet foralkaline water in the alkaline water delivery mode but operating as theoutlet for acidic water in the acidic water delivery mode, the secondoutlet serving as the outlet for acidic water in the alkaline waterdelivery mode but serving as the outlet for alkaline water in the acidicwater delivery mode. The inlet 70 is in fluid communication with aplenum chamber or water distribution passage 76 of a generallytriangular cross-section. As best shown in FIG. 7, the plenum chamber 76is defined by the casing 56 and the cover 66 and extends throughout theentire vertical length of the electrodes.

As shown enlarged in FIG. 10, a pair of flow paths 78 are formed on bothsides of the central electrode 60. Each of the flow paths concerts withthe electrodes to operate as the electrolytic chamber. A plurality ofhorizontally extending spacers 64 are sandwiched between the electrodesto ensure that water flowing down along the plenum chamber 76 flows intothe flow paths 78 in the horizontal direction as shown in FIG. 10. Sincethe electrode spacing is so small as 0.5 mm, a laminar flow isestablished in the flow of water flowing through the flow paths 78 inthe horizontal direction. Accordingly, acidic water and alkaline waterwhich are generated respectively along the surfaces of the electrodes byelectrolysis can be recovered separately, without providing a membranebetween electrodes.

Electrolyzed water produced along the surfaces of the central electrode60 is collected in a first collection passage 80 for electrolyzed waterand is delivered through the first outlet 72. The first collectionpassage 80 is defined by the casing 56 and the cover 66 and extendsthroughout the entire vertical length of the electrodes in a mannersimilar to the plenum chamber 76. Electrolyzed water produced along thesurfaces of the lateral electrodes 58 and 62 is recovered in secondcollection passages 82 for electrolyzed water. To this end, each of thelateral electrodes is provided with a slit 84 to ensure that the flow ofelectrolyzed water flowing along the surfaces of the lateral electrodes58 and 62 is directed to flow into the second collection passages 82.Electrolyzed water recovered in the second collection passages 82 isforwarded to a connection port 86 for delivery from the second outlet74.

Referring again to FIG. 4, a valve unit 88 is connected to the bottom ofthe electrolytic cell 36 so as to control the direction of two kinds ofelectrolyzed water (acidic water and alkaline water) flowing out of theoutlets 72 and 74 of the cell 36. The valve unit 88 may be comprised ofa rotary flow control valve 90 having a flow rate control function andan electrically driven actuator 92. A flow sensor for detecting the flowrate through the water processing unit 10 may be incorporated in thevalve unit 88.

Referring further to FIG. 4, a control and display section 94 isprovided at the base 40 of the processing unit 10. Also arranged withinthe base 40 is a control unit which is designed to control the electricheater 46 for regenerating activated carbon of the processing unit 10,the electrolytic cell 10 and a motor of the actuator 92.

An example of the layout of the control and display section 94 is shownin FIG. 11. The control and display 94 may include a manual regenerationcontrol switch 96 for commencing regeneration of activated carbon in thecartridge 34 in accordance with the instructions of the user, aregeneration time set switch 98 for setting the time at whichregeneration of activated carbon is commenced in an automaticregeneration mode, a liquid crystal display panel 100, selectionswitches 102 and 104 to enable the user to select the kind of water tobe delivered, and light emitting diodes 106 for indicating the selectedwater.

In the illustrated layout, the control and display section 94 isdesigned such that by operating the selection switch 102 or 104 the usermay select either purified water processed by the filter 32 and theactivated carbon cartridge 34, or acidic or alkaline water obtained bysubjecting purified water further to electrolysis. The pH of alkalinewater may be adjusted in three different levels including strong, mediumand weak. The arrangement may be such that, for example, weakly acidicwater of pH 6.5 is obtained in the acidic water delivery mode, whereasalkaline water of pH 8.5, pH 9.0 or pH 9.5 is obtained in the alkalinewater delivery mode.

In FIG. 12, there is shown an embodiment of the control unit of thewater processing unit 10. An electric power is applied to the controlunit 108 from a commercial AC power source 112 via a cable 110 (FIG. 3).The control unit 108 includes a programmed microcomputer 114 which isprogrammed in such a manner as to control the power as well as thepolarity of the direct current supplied to the electrolytic cell 36, tocontrol the motor of the actuator 92 for switching the destination ofwater delivered from the cell 36, and to control the power supply to theheater 46 intended to regenerate the activated carbon cartridge 34.

The control unit 108 has a diode bridge 116 for full-wave rectifying thealternating current from the power source 112 and a switching powercircuit 118. Briefly, the control unit 108 is designed and constructedsuch that in accordance with various operating parameters themicrocomputer 114 theoretically computes the desired power consumptionof the electrolytic cell 36 and that the microcomputer 114 feed-backcontrols the switching power circuit 118 in such a manner that the poweractually supplied to the cell is equal to the desired power consumption.More specifically, the switching power circuit 118 includes aphotocoupler 120, a capacitor 122 for smoothing the output of thelatter, an integrated circuit 124 having a pulse width modulationfunction, a switching transistor 126 and a switching transformer 128.

The alternating current from the commercial power source 112 isfull-wave rectified by the diode bridge 116, the DC output of which isapplied to the primary winding of the switching transformer 128. Thepulse width of the direct current flowing the primary windings of theswitching transformer 128 is controlled by the switching transistor 126driven by the IC 124 so that an electric current having a wattageproportional to the pulse duty of the primary windings is induced in thesecondary winding of the switching transformer 128. The secondarywinding of the switching transformer 128 is connected to the electrodesof the electrolytic cell 36 through a reversal switch 130 designed toreverse the polarity of the voltage. The reversal switch 130 iscontrolled by a relay 132 which is in turn controlled by themicrocomputer 114.

A resistor 134 for detecting the intensity of current flowing throughthe cell is connected in series to the lead wires connecting the cell 36and the switching transformer 128, and a pair of resistors 136 fordetecting the voltage applied to the cell are connected in parallel tothe lead wires. The junctions to these resistors 134 and 136 areconnected to input terminals of analog-to-digital converter of themicrocomputer to ensure that the microcomputer 114 periodically checksthe potential at these junctions to detect the intensity and the voltageof electric current supplied to the electrolytic cell.

The control unit 108 further includes a solid state relay (SSR) 138 forcontrolling power supply to the heater 46 for regenerating activatedcarbon, the relay being adapted to be controlled by the microcomputer114. A thermistor 140 is held in contact with the bottom of theactivated carbon cartridge 34 to detect the temperature of the cartridgebottom, the output signal of the thermistor 140 being applied to themicrocomputer 114.

The valve unit 88 is provided with a flow sensor 142 for detecting theflow rate of water flowing through the water processing unit 10, theoutput of the sensor being applied to the microcomputer 114. The flowsensor 142 is used to detect the cumulative amount of feed to theprocessing unit 10, to determine the desired power consumption inaccordance with the detected flow rate, and to detect the presence orabsence of water feed. However, in the case that only the presence orabsence of water feed is to be detected, a pressure sensor responsive towater pressure may by used in lieu of the flow sensor 142.

Through a motor driver circuit, the microcomputer 114 drives the motorof the actuator 92 having a reduction gear mechanism. A rotary encoderincorporated in the actuator 92 detects the angular position of thefinal stage output shaft of the reduction gear mechanism and sends asignal to the microcomputer 114. The microcomputer 114 controls theactuator 92 in response to the signal from the rotary encoder to therebycontrol the rotary valve 90 whereby the destination of two kinds ofelectrolyzed water (acidic water and alkaline water) flowing out of theoutlets 72 and 74 of the cell 36 is changed over.

To describe the mode of operation and use of the water processing unit10, when the user operates the control switch 102 or 104 to select"purified water", the microcomputer 114 drives the actuator 92 until thetwo outlets 72 and 74 of the cell 36 are connected to the water deliveryhose 24.

In this mode wherein purified water is delivered, no electric power isapplied to the electrolytic cell 36. As the user rotates the handle 26(FIG. 3) to connect the valve 16 to the water processing unit 10 andopens the valve 16, tap water is purified as it flows through thehollow-fiber membrane filter 32 and the activated carbon cartridge 34 sothat purified water is sent through the cell 36, which is nowinactivated, to the water delivery hose 24 for delivery from the outlet28.

If the user selects "alkaline water", the flow control valve 90 will berotated into such a position wherein the first outlet 72 of the cell 36is connected to the delivery hose 24, with the second outlet 74 of thecell 36 connected to the drain hose 30, and wherein the flow rate ofwater flowing from the first outlet 72 of the cell 36 to the deliveryhose 24 is equal to 4 liters per minute and the flow rate of waterflowing from the second outlet 74 of the cell 36 to the drain hose 30 isequal to 1 litter per minute.

In the alkaline water delivery mode, an electric potential of about 8Vis applied to the electrolytic cell 36 in such a polarity that thecentral electrode 60 functions as the cathode and the lateral electrodes58 and 62 serve as the anode. As a result, alkaline water is generatedalong the surfaces of the cathode 60 and is forwarded to the firstoutlet 72 of the cell, with acidic water being produced along thesurfaces of the anodes 58 and 62 and forwarded to the second outlet 74.The power supply to the cell 36 is controlled by the microcomputer 114such that water of the desired pH (e.g., pH 8.5, pH 9.0 or pH 9.5)selected by the user is delivered. Alkaline water thus produced is sentvia the delivery hose 24 to the faucet spout.

The embodiment shown is designed so that acidic water produced duringoperation in the alkaline water delivery mode is discharged through thedrain hose 30 into the sink. It will be noted, however, that in thismode strongly acidic water containing hypochlorous acid and chlorine gasis generated along the anodes 58 and 62 upon electrolysis of sodiumchloride. Strongly acidic water containing hypochlorous acid andchlorine gas will similarly be produced if salt is added to incomingwater. Such strongly acidic water sent to the drain hose 30 isbactericidal and may be recovered from hose 30 for use as germicidalwater.

When the user has selected "acidic water", the relay 132 is energized toswitch over the reversal switch 130 so that an electric power issupplied to the cell 36 in such a polarity that the central electrode 60acts as the anode and the lateral electrodes 58 and 62 serves as thecathode. Accordingly, acidic water is obtained at the first outlet 72 ofthe cell 36 and alkaline water is delivered from the second outlet 74.The flow control valve 90 is rotated into a position wherein the flowrate of water flowing from the first outlet 72 of the cell 36 to thedelivery hose 24 is equal to 3 liters per minute and the flow rate ofwater flowing from the second outlet 74 of the cell 36 to the drain hose30 is equal to 2 liters per minute.

As the electrolytic cell 36 is operated, calcium carbonate and the likewill precipitate on the surface of the electrode which has been servedas the cathode. Therefore, according to the invention, an electricpotential of the polarity which is in reverse to the polarity of theprevious operation is periodically applied to dissolve precipitates tothereby remove scale. It is preferable that the descaling operation byway of reverse potential application is carried out automaticallywhenever the preset time for regeneration of activated carbon fixed bythe regeneration time set switch 98 has arrived. This is because theuser is generally recommended to preset the regeneration time at atiming, such as at night, at which the water processing unit 10 is notin use.

Preferably, water that flows out of the cell 36 during descaling isdiscarded since it contains dissolved substances and, hence, is notproper to drink. Accordingly, upon arrival of the preset time, the flowcontrol valve 90 is rotated to a position in which the totality of waterissuing from the cell 36 is forwarded to the drain hose 30. Themicrocomputer 114 then checks the signal from the flow sensor 142 to seeif water is being fed to the processing unit 10. In the absence of waterfeed, the reversal switch is reversed further from the position of theprevious operation so as to apply to the electrodes of the cell 36 anelectric potential having a polarity which is in reverse to the polarityof the previous operation. While it will suffice that application of thereverse potential is carried out for about a second, it may be continuedfor about 5 minutes. Upon application of the reverse voltage,precipitates deposited on the electrodes during the previous sequence ofgenerating alkaline or acidic water will be released from the electrodesas mentioned before.

Upon completion of the application of reverse potential, themicrocomputer 114 of the control unit 108 commences power supply to theheater 46 of the cartridge 34. As the heater 46 is energized, water inthe cartridge boils up so that activated carbon in the cartridge 34 isboiled and sterilized. At the same time, chlorine ions and volatilesubstances such as trihalomethanes adsorbed by the activated carbon aredesorbed so that activated carbon is regenerated. The temperature at thebottom of the cartridge 34 detected by the thermistor 140 will be raisedas water in the cartridge 34 and water impregnated in the activatedcarbon are evaporated. Upon sensing that the bottom of the cartridgeexceeds, for example, 120° C., the microcomputer 114 terminates powersupply to the heater 46.

EXAMPLE

The membraneless electrolytic cell as shown in the accompanying drawingswas build and was subjected to an accelerated test which is equivalentto 7 years of operation and wherein tap water of Chigasaki City of Japancontaining about 20 ppm of calcium ion was electrolyzed while performingthe reverse electrolysis descaling by applying reverse potential. Aftereach sequence of electrolysis for from 1 to 30 minutes at a flow rate ofalkaline water of 4 liters per minute and a flow rate of acidic water of1 liter per minute, the reverse electrolysis descaling by application ofreverse polarity potential was carried out for 0 to 300 seconds eitherin the stopped or flowing water condition. The effect of the reverseelectrolysis descaling was assessed in two aspects; whether alkalinewater of the desired pH value (pH 9.5) was obtainable and whether therewas prescriptation of the scale. The results are shown in the followingtables wherein the mark "X" indicates that formation of prescipitatesoccurred and that the pH was lowered, while the mark "O" represents thatno precipitate was observed and that the pH remained stable.

    ______________________________________                                        Duration of   Duration of Electrolysis (min)                                  Descaling (sec)                                                                             1     4          15  30                                         ______________________________________                                        a) Reverse Electrolysis Descaling under Stopped Water                         0             X     X          X   X                                          1             ◯                                                                       ◯                                                                            ◯                                                                     X                                          30            ◯                                                                       ◯                                                                            ◯                                                                     ◯                              300           ◯                                                                       ◯                                                                            ◯                                                                     ◯                              b) Reverse Electrolysis Descaling under Flowing Water                         0             X     X          X   X                                          1             X     X          X   X                                          30            ◯                                                                       ◯                                                                            X   X                                          300           ◯                                                                       ◯                                                                            ◯                                                                     X                                          ______________________________________                                    

From the tables above, it will be noted that the formation ofprecipitates is very little in the case where the reverse electrolysisdescaling is carried out while water feed through the cell is stopped.For example, deposition of precipitate may be avoided for 7 yearsprovided that 30 seconds of reverse electrolysis descaling is carriedout under stopped water condition after every 30 minutes ofelectrolysis.

In summary, according to the invention, scale such as calcium carbonateis effectively removed without shortening the life of the electrodes. Asa result, the overall life of the electrolytic cell is remarkablyextended. In fact, according to the invention, the life of theelectrolytic cell was prolonged up to about 7 years.

While the present invention has been described herein with reference tothe specific embodiments thereof, it is contemplated that the inventionis not limited thereby. For example, the filtration stage 32 and theactivated carbon cartridge 34 of the water processing unit 10 may beomitted and the design and structure of the electrolytic cell 36 may bechanged or modified. The cycle and frequency of reverse potentialapplication may be altered as required.

We claim:
 1. A method for electrolyzing water that extends the life ofthe electrodes, characterized by repeating in sequence the stepsof:subjecting water to electrolysis by feeding water through anelectrolytic cell having a pair of electrodes facing with each otherwithout intervention of a membrane therebetween and by applying a DCpotential of a first polarity between said electrodes; and removingprecipitates deposited on the electrodes during the preceding step bystopping feed of water through the cell and by applying a DC potentialof a second polarity opposite the first polarity between said electrodeswhile water between the electrodes stays stagnant and wherebyprecipitates are dissolved into the stagnant water.
 2. A method forelectrolyzing water according to claim 1, wherein said step of removingprecipitates is carried out at least once a day.
 3. A method forelectrolyzing water according to claim 2, wherein application of thepotential of an opposite polarity in said step of removing precipitatesis carried out each time for at least about a second.
 4. An apparatusfor electrolyzing water that extends the life of the electrodes,comprising:a membraneless electrolytic cell having a pair of electrodesand through which water is fed; a DC power source for applying a DCpotential between said electrodes; a reversal switch for reversing thepolarity of potential applied between the electrodes; detecting meansfor detecting feed of water through the cell; and, control means, havinga timer function, for controlling said reversal switch in response tosaid detecting means; said control means controlling said reversalswitch in such a manner that a DC potential of a first polarity isapplied between the electrodes while water is fed through the cell andthat after the feed of water through the cell is stopped a DC potentialof a second polarity opposite the first polarity is applied to stagnantwater between the electrodes for a time sufficient to dissolveprecipitants into the stagnant water.
 5. An apparatus for electrolyzingwater according to claim 4, wherein said control means operates saidreversal switch such that a DC potential of the second polarity isapplied between the electrodes everyday at night for a period of timewhen feed of water through the cell is stopped.